This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Digital Light Processing (“DLP”) is a display technology that employs an optical semiconductor, known as a Digital Micromirror Device (“DMD”) to project video onto a screen. DMDs typically contain an array of at least one million or more microscopic mirrors mounted on microscopic hinges. Each of these mirrors is associated with a point on the screen, known as a pixel. By varying the amount of light that is reflected off each of these mirrors, it is possible to project video onto the screen. Specifically, by electrically actuating each of these hinge-mounted microscopic mirrors, it is possible to either illuminate a point on the screen (i.e., “turn on” a particular micromirror) or to leave that particular point dark by reflecting the light somewhere else besides the screen (i.e., “turn off” the micromirror). Further, by varying the amount of time a particular micromirror is turned on, it is possible to create a variety of gray shades. For example, if a micromirror is turned on for longer than it is turned off, the pixel that is associated with that particular micromirror, will have a light gray color; whereas if a particular micromirror is turned off more frequently than it is turned on, that particular pixel will have a darker gray color. In this manner, video can be created by turning each micromirror on or off several thousand times per second. Moreover, by shining colored light at the micromirrors instead of white light, it is possible to generate millions of shades or color instead of shades of gray.
As stated above, the shading of a particular pixel may be partially determined by the length of time that the micromirror corresponding to that pixel is either turned on or turned off. However, as described above, the micromirrors are hinge mounted. As such, there are electrical and mechanical constraints inherent to turning on or turning off a particular micromirror. For example, in current generation DMDs, the minimum amount of time that one of the micromirrors can be turned on is approximately fifteen microseconds. This minimum amount of time is known as the least significant bit (“LSB”). While succeeding generations of DMD technology may reduce this minimum time threshold, it cannot be eliminated, and there are a variety of shades of color that correspond to turning the micromirror on for somewhere between zero seconds and this minimum time threshold (currently fifteen microseconds). These particular shades present special challenges for DLP-based video units.
Dithering is one method to overcome the above described challenges. Dithering involves fooling the eye of the viewer by rapidly turning a micromirror on and then off, such that the mind of viewer blurs the turned on shade and the turned off shade (i.e., black) together to form a shade that corresponds to turning on one of the micromirrors for less than fifteen microseconds. While dithering does increase the number of shades that the DLP system can display, it may cause additional noise, known as either dithering noise or error diffusion noise. This dithering noise reduces the quality of the television picture and in some cases may even be overtly visible to a viewer. Reducing this dithering noise is desirable.